Method for producing resistances of the multi-layer type



March 18, 1969 TAKEQ YAMADA METHOD FOR PRODUCING RESISTANCES OF THE MULTI-LAYER TYPE Filed April 5, 1967 FIG. 1 DJ 3 R0 LLI o 2 ,5 R1 2 (D i Rn Rnmax (AXIAXZ 2751 O DISTANCE FROM THE BASE POINT X BASE POINT FIG. 3 nr x ---m=nmox Sheet of 2 FIG.2

DISITANCE FRPM 1THE BASE POINT X &|%- THICKNESS or METAL FILM XI AXZ Axn (LENGTH OF n DIVISION) March ,1969 'TAKEo Y AMAD A 3,432,922

METHOD FOR PRODUCING RESISTANCES OF THE MULTI-LAYER TYPE Filed April 5, 1967 Sheet 2 of 2 FIGQH M u 12 13 14 15 i6 17 i8 19 20 OBLIQUE-LINE PORTIONS ARE THOSE SHIE- LDED BY MASK F IG, 6 ORDER OF THICKNESS OF EVAPORATION EVAPORATION Hm) m=s (2 -'=4 m=2 (QM-52) m=1 (2""=| A LLI z FIG. 8 E Q U) LLI FIG 7 LL W O n R 5 r r x i L Y1 F2 F3 fa Y5 r r 1 Yn+1 n n+1 Patented Mar. 18, 1969 Claims The present invention relates to a method for producing variable resistances of the multi-layer type by the successive deposition of metal films.

Process for manufacturing multilayered resistances in which the number of successive depositions of metal films is less than the number of portions or divisions of the resistance. The variable resistances produced by the hereinafter disclosed method are directed primarily, but not necessarily the variable resistance used for exposure exclusively, for use with exposure meters. Such variable resistances must have wide variable ranges and at the same time, must be resistant to wear by the moving brush, and must be easily produced.

In accordance with the conventional methods such variable resistances have been prepared by coating carbon film in a number of layers. However, the stability of carbon film is poor, and at the same time such variable resistances are easily worn out. In order to overcome these drawbacks, metal film multilayer variable resistances have been produced by vacuum evaporation of metal film. Present day methods of producing multilayered resistances by vacuum evaporation are carried out layer by layer, and this is expensive and time consuming.

The present invention is to provide the method for producing variable resistances according to which the number of vacuum evaporation operations is reduced and yet maintaining the excellent quality of the resistances thus obtained.

In accordance with the present invention, a method is provided for producing resistances of the multilayered type in which successive metal film deposits are made, preferably by vacuum evaporation methods on an insulating base plate. At least one mask is provided to shield the divisions or portions of the resistance in which a positive integer represented by N in the formula given below does not become an odd number, and only exposes other divisions in which the integer N becomes an odd number, or

wherein the number of the required divisions to be set up is n, and the order of vacuum evaporations when counted from the lowest first layer is set up to be m, then carrying out vacuum evaporation for m times determined by the formula of 2 n;2 while controlling the thickness of the layer deposited through the mask to be 2 times of the thickness of the first or lowermost layer (m=l), and electrically connecting the respective adjacent divisions by allowing slight overlaid or overlapping portions, respectively.

The objects, advantages and features of the present invention will become more apparent by the following explanation comparing the present method with a conventional method, and by referring to an illustrative embodiment of the present invention shown in the accompanied drawing, in which:

FIG. 1 is a curve showing the relation between a distance x measured from the base point of a resistance piece and a value of resistance R;

FIG. 2 is a curve showing dR/dX of the resistance value It shown in FIG. 1 and showing its stepwise approximat1on state;

FIG. 3 shows a conventional process for carrying out vacuum evaporation of metal film;

FIG. 4 represents the equivalent electrical circuit of FIG. 3;

FIG. 5 shows a variable resistance in its completed state;

FIG. 6 shows an illustrative embodiment of the process of the present invention;

FIG. 7 represents the equivalent electrical circuit of FIG. 6;

FIG. 8 is a curve showing the relation between a distance x measured film the base point and the values of resistance showing the changes of the resistance at the division border portion in accordance with the present invention;

FIG. 9 shows a plan view of a ring-formed resistance piece produced by the present invention;

FIG. 10 shows an embodiment of a mask for making the resistance piece of FIG. 9; and

FIG. 11 is a table showing an example of thicknesses T(m) of the vacuum evaporation in the respective resistance divisions.

One usual way of making variable resistances according to known methods is carried out in the following manner:

(1) The point where the value of resistance becomes maximum is set up to be the base point, and as is shown in FIG. 1(a) the relation between a distance x from the base point and the value of resistance R is determined.

(2) Then as is shown in FIG. 2(b), the relation between dR/dX and the distance x from the base point is derived.

(3) The dR/dX curve is changed into a stage-form or stepped straight line approximating the curve. In other words, in accordance with the required precision, a constant width t (an appropriate value) is set up in the dR/dX direction as shown in FIG. 2(c), and the length of the respective stage AXn (the respective stages can be diflerent) in the direction of x axis is determined.

The notation t is a unit thickness of the metal film which has the relation as given below, and shows the value on the axis;

wherein b stands for the width of the resistance piece; and p stands for the specific resistance of the metal substance.

(4) The values of p and b are selected so as to satisfy the below given formula nmax. pbt 2 AXn=R R,, max. (the range of resistance) Thus, in the production multilayered resistances, the following steps are taken:

As is shown in FIG. 3, metal film 2 having a unit thickness of t is adhered for m times over the 1st division to the n max.th division by means of vacuum evaporation. In this case, the condition of lgmgn max. must be satisfied.

The resistance is completed, as shown in FIG. 5, after the vacuum evaporations are repeated for m=n max. times (no special order being required). The resistance circuit in this case can be considered to be the equivalent circuit as is shown in FIG. 4, in which r =pbt.

According to the present invention, the following method for the production of variable resistors is carried out:

(A) First, the required resistance division or portion number is assumed to be n, and the order of the vacuum evaporation when counted from the lowest layer is assumed to be m. The required number and kinds of masks which shield the portions or divisions wherein the positive integer represented by N does not become an odd number in the formula given below, and only expose the portions or divisions where the integer represented by N becomes an odd number, are prepared. This relationship as hereinabove set forth is In the present method, consideration is given in advance so that the area of the division exposed by the masks is slightly overlaid or overlapping the edges of adjacent divisions.

(B) Next, the relation between the order m of the vacuum evaporation and the thickness of the corresponding vacuum evaporation T(m)-which is controlled by the time of vacuum evaporation-can be determined by the relation represented by the formula:

wherein t stands for the unit thickness of the vacuum evaporation film.

The thickness T(m) of the successive deposits of the respective resistance divisions under the conditions (A) and (B), may be given actual values as exemplified in the table of FIG. 11. For example, with regard to the resistance divisions n=7 as shown in FIG. 6, the first layer whose thickness is t is vacuum evaporated on the divisions (n=1.3.5.7) as determined by the first mask, and then the second layer whose thickness is 2t is vacuum evaporated on the divisions (n=2.3.6.7) as determined by the second mask, and last of all-the third layer whose thickness is 4t is vacuum evaporated on the divisions (n=4.5.6.7) as determined by the third mask. As a result thereof, the metal films, the thickness thereof being respectively t, 2t, 3t 7t, are formed on the respective resistance divisions (1 through 7), and thickness of the final product becomes equal or similar as shown in FIG. 5. In this case, the resistance of the overlaid or overlapping portion (w) of the films which is produced at the joint portion between the respective divisions as shown in FIG. 6, is small compared to the other resistances, as is shown in 'FIG. 8, so that the electrical effects thereof may be ignored. With regard to the mechanical effect generated from the relation thereof to the moving brush, there is no diificulty because the thickness of the film itself is just several microns to several ten microns.

When the number of the stages of the resistance divisions is n, it has hitherto been necessary to carry out the processes of vacuum evaporation for n times in accordance with the conventional methods. In accordance with the method of the present invention the number m of the repeated vacuum evaporations is reduced considerably as is apparent from the formula;

An embodiment is given in FIG. 9 and FIG. 10 wherein the ring form resistance piece is prepared, and the fundamental technique for producing the same is exactly the same as mentioned above.

From the foregoing, it is apparent that when the method of the present invention is employed, it is possible to greatly reduce the number of vacuum evaporation operations. The present invention is very advantageous when applied in the production of multilayered resistances from the standpoint of cost, time and reliability of the resultant product in actual use.

What is claimed is:

1. Process for manufacturing a multilayered resistance on an insulating base plate by the sequential deposit of metal films to provide divisions or portions for the resistance, comprising the steps of successive shielding divisions or portions with a mask in which a positive integer N remains an even number and exposes only divisions or portions in which the integer N becomes an odd member determined by where n is the required number of divisions or portions, and m is the order of deposition from the lowermost layer, then depositing successive film layers through the exposing portions of successive masks in accordance with the relationship of and controlling the thickness of each film layer according to 2 times the thickness of the lowermost layer.

2. Process according to claim 1, wherein the film layers are deposited with overlaid or overlapping portions to electrically interconnect the divisions or portions.

3. Process according to claim 1, wherein the number of portions is 7 and the number of film depositions is 3, the first mask during the first deposition permitting film deposits on divisions 1, 3, 5 and 7, the second mask during the second deposition permitting film deposits on divisions 2, 3, 6 and 7, and the third mask during the third film deposition permitting film deposits on divisions 4, 5, 6 and 7, and wherein the successive depositions of the films are continued until the thickness of the third film deposited is twice the thickness of the second film deposited and four times the thickness of the first film deposited.

References Cited UNITED STATES PATENTS 1,889,379 11/1932 Ruben 338142 X 2,963,675 12/1960 Rannie 338-115 X 3,325,763 6/1967 Casey 338-142 X 3,390,453 7/ 1968 Riddle 29620 JOHN CAMPBELL, Primary Examiner.

I. L. CLINE, Assistant Examiner.

US. Cl. X.R. 338142 

1. PROCESS FOR MANUFACTURING A MULTILAYERED RESISTANCE ON AN INSULATING BASE PLATE BY THE SEQUENTIAL DEPOSIT OF METAL FILMS TO PROVIDE DIVISIONS OR PORTIONS FOR THE RESISTANCE, COMPRISING THE STEPS OF SUCCESSIVE SHIELDING DIVISIONS OR PORTIONS WITH A MASK IN WHICH A POSITIVE INTEGER N REMAINS AN EVEN NUMBER AND EXPOSES ONLY DIVISIONS OR PORTIONS IN WHICH THE INTEGER N BECOMES AN ODD MEMBER DETERMINED BY N<=N/2**(M-1)<N+1 WHERE N IS THE REQUIRED NUMBER OF DIVISIONS OR PORTIONS, AND M IS THE ORDER OF DEPOSITION FROM THE LOWERMOST LAYER, THEN DEPOSITING SUCCESSIVE FILM LAYERS THROUGH THE EXPOSING PORTIONS OF SUCCESSIVE MASKS IN ACCORDANCE WITH THE RELATIONSHIP OF 2**M>N>=2**(M-1) AND CONTROLLING THE THICKNESS OF EACH FILM LAYER ACCORDING TO 2**(M-1) TIMES THE THICKNESS OF THE LOWERMOST LAYER. 